Haskell

Plenty of scope for making part 2 faster, but I think simple is best here. Forgot to sort the lists in the first part, which pushed me waaay off the leaderboard.

import Data.List

main = do
  [as, bs] <- transpose . map (map read . words) . lines <$> readFile "input01"
  print . sum $ map abs $ zipWith (-) (sort as) (sort bs)
  print . sum $ map (\a -> a * length (filter (== a) bs)) as

Uiua

For entertainment purposes only, I’ll be trying a solution in Uiua each day until it all gets too much for me…

$ 3   4
$ 4   3
$ 2   5
$ 1   3
$ 3   9
$ 3   3
⊜∘⊸≠@\n     # Partition at \n.
⊜(⍆∵⋕)⊸≠@\s # Partition at space, parse ints, sort.

&p/+/(⌵-). # Part1 : Get abs differences, sum, print.

&p/+×⟜(/+⍉≡⌕)°⊂ # Part 2 : Count instances, mul out, sum, print.

TypeScript

import { AdventOfCodeSolutionFunction } from "./solutions";

function InstancesOf(sorted_array: Array<number>, value: number) {
    const index = sorted_array.indexOf(value);
    if(index == -1)
        return 0;

    let sum = 1;

    for (let array_index = index + 1; array_index < sorted_array.length; array_index++) {
        if(sorted_array[array_index] != value)
            break;

        sum += 1;
    }

    return sum;
}

export const solution_1: AdventOfCodeSolutionFunction = (input) => {
    const left: Array<number> = [];
    const right: Array<number> = [];

    const lines = input.split("\n");

    for (let index = 0; index < lines.length; index++) {
        const element = lines[index].trim();
        if(!element)
            continue;

        const leftRight = element.split("   ");
        left.push(Number(leftRight[0]));
        right.push(Number(leftRight[1]));
    }

    const numSort = (a: number, b: number) => a - b;
    left.sort(numSort);
    right.sort(numSort);

    let sum = 0;
    for (let index = 0; index < left.length; index++) {
        const leftValue = left[index];
        const rightValue = right[index];

        sum += Math.abs(leftValue - rightValue);
    }

    const part1 = `Part 1: ${sum}`;

    sum = 0;
    for (let index = 0; index < left.length; index++) {
        sum += left[index] * InstancesOf(right, left[index]);
    }

    const part2 = `Part 2: ${sum}`;

    return `${part1}\n${part2}`;
};

Nim

I’ve got my first sub-1000 rank today (998 for part 2). Yay!
Simple and straightforward challenge, very fitting for 1st day. Gonna enjoy it while it lasts.

proc solve(input: string): AOCSolution[int, int] =
  var l1,l2: seq[int]
  for line in input.splitLines():
    let pair = line.splitWhitespace()
    l1.add parseInt(pair[0])
    l2.add parseInt(pair[1])
  l1.sort()
  l2.sort()

  block p1:
    for i in 0..l1.high:
      result.part1 += abs(l1[i] - l2[i])

  block p2:
    for n in l1:
      result.part2 += n * l2.count(n)

Codeberg repo

Rust

Right IDs are directly read into a hash map counter.

use std::str::FromStr;
use std::collections::HashMap;

fn part1(input: String) {
    let mut left = Vec::new();
    let mut right = Vec::new();
    for line in input.lines() {
        let mut parts = line.split_whitespace()
            .map(|p| u32::from_str(p).unwrap());
        left.push(parts.next().unwrap());
        right.push(parts.next().unwrap());
    }
    left.sort_unstable();
    right.sort_unstable();
    let diff: u32 = left.iter().zip(right)
        .map(|(l, r)| l.abs_diff(r))
        .sum();
    println!("{diff}");
}

fn part2(input: String) {
    let mut left = Vec::new();
    let mut right: HashMap<u32, u32> = HashMap::new();
    for line in input.lines() {
        let mut parts = line.split_whitespace()
            .map(|p| u32::from_str(p).unwrap());
        left.push(parts.next().unwrap());
        *right.entry(parts.next().unwrap()).or_default() += 1;
    }
    let similar: u32 = left.iter()
        .map(|n| n * right.get(n).copied().unwrap_or_default())
        .sum();
    println!("{similar}");
}

util::aoc_main!();

Smalltalk

day1p12: input    
	| list1 list2 nums dist sim |
	
	list1 := OrderedCollection new.
	list2 := OrderedCollection new.
	
	input linesDo: [ :l |
		nums := l substrings collect: [ :n | n asInteger ].
		list1 add: (nums at: 1).
		list2 add: (nums at: 2).
	].

	list1 sort.
	list2 sort.
	
	dist := 0.
	list1 with: list2 do: [ :a :b | dist := dist + (a - b) abs ].
	
	sim := list1 sumNumbers: [ :x | x * (list2 occurrencesOf: x) ].
	
	^ Array with: dist with: sim.

Not going to push hard on these first days (fever being a reason), so I slept in quite a bit before looking at the problem.

List<int> _LeftList = new List<int>();
List<int> _RightList = new List<int>();

// Fed via File.ReadLines(...).Select(l => l.Trim())
public void Input(IEnumerable<string> lines)
{
  foreach (var line in lines)
  {
    var split = line.Split(' ', StringSplitOptions.RemoveEmptyEntries).Select(s => int.Parse(s));
    _LeftList.Add(split.First());
    _RightList.Add(split.Last());
  }
}

public void Part1()
{
  Console.WriteLine($"Sum: {_LeftList.Order().Zip(_RightList.Order()).Select(v => Math.Abs(v.First - v.Second)).Sum()}");
}
public void Part2()
{
  Console.WriteLine($"Sum: {_LeftList.Select(l => _RightList.Where(i => i == l).Count() * l).Sum()}");
}

I’m quite inexperienced as a programmer, I learned most of the basic concepts from playing human resource machine and 7 billion humans. After mucking about writing some CLI utilities in Perl and python, I’ve decided to give rust a go.

Part 1

Part 2

C#

public class Day01 : Solver
{
  private ImmutableArray<int> left;
  private ImmutableArray<int> right;

  public void Presolve(string input)
  {
    var pairs = input.Trim().Split("\n").Select(line => Regex.Split(line, @"\s+"));
    left = pairs.Select(item => int.Parse(item[0])).ToImmutableArray();
    right = pairs.Select(item => int.Parse(item[1])).ToImmutableArray();
  }

  public string SolveFirst() => left.Sort().Zip(right.Sort()).Select((pair) => int.Abs(pair.First - pair.Second)).Sum().ToString();

  public string SolveSecond() => left.Select((number) => number * right.Where(v => v == number).Count()).Sum().ToString();
}

Python

left_list = []
right_list = []

for line in file:
    split_line = line.split()
    left_list.append(int(split_line[0]))
    right_list.append(int(split_line[1]))

sorted_left = sorted(left_list)
sorted_right = sorted(right_list)
distance = []
for left, right in zip(sorted_left, sorted_right):
    distance.append(abs(left - right))

total = sum(distance)

print(total)

file = open('input.txt', 'r')
left_list = []
right_list = []

for line in file:
    split_line = line.split()
    left_list.append(int(split_line[0]))
    right_list.append(int(split_line[1]))

sim_score = 0
for item in left_list:
    sim = right_list.count(item)
    sim_score += (sim * item)

print(sim_score)

I am sure there were better ways to do this, this was just the first way in my head, in the order it appeared

Solution in C

Part 1 is a sort and a quick loop. Part 2 could be efficient with a lookup table but it was practically instant with a simple non-memoized scan so left it that way.

Kotlin

No 💜 for Kotlin here?

import kotlin.math.abs

fun part1(input: String): Int {
    val diffs: MutableList<Int> = mutableListOf()
    val pair = parse(input)
    pair.first.sort()
    pair.second.sort()
    pair.first.forEachIndexed { idx, num ->
        diffs.add(abs(num - pair.second[idx]))
    }
    return diffs.sum()
}

fun part2(input: String): Int {
    val pair = parse(input)
    val frequencies = pair.second.groupingBy { it }.eachCount()
    var score = 0
    pair.first.forEach { num ->
        score += num * frequencies.getOrDefault(num, 0)
    }
    return score
}

private fun parse(input: String): Pair<MutableList<Int>, MutableList<Int>> {
    val left: MutableList<Int> = mutableListOf()
    val right: MutableList<Int> = mutableListOf()
    input.lines().forEach { line ->
        if (line.isNotBlank()) {
            val parts = line.split("\\s+".toRegex())
            left.add(parts[0].toInt())
            right.add(parts[1].toInt())
        }
    }
    return left to right
}

Viml

I think viml is a very fun language, i like weird languages lol, so this year im doing it in viml while trying to use as many of the original ed/ex commands as i can (:d, :p, :a, :g, …)

!cp ./puzzle1 ./puzzle1.editing
e ./puzzle1.editing

1,$sort
let row1 = []

g/^\d/let row1 = add(row1, str2nr(expand("<cword>"))) | norm 0dw
1d
1,$sort
g/^\d/execute 'norm cc' .. string(abs(expand("<cword>") - row1[line('.') - 1]))

$a|---ANSWER---
0
.
1,$-1g/^\d/call setline("$", str2nr(getline("$")) + str2nr(expand("<cword>")))

read ./puzzle1

let cnt = 0
g/^\d/let cnt += expand("<cword>") *
            \ searchcount(#{pattern: '\s\+' .. expand("<cword>")}).total

echo cnt .. "\n"

w! ./puzzle1.editing

Rust

I’m doing it in Rust again this year. I stopped keeping up with it after day 3 last year, so let’s hope I last longer this time around.

use std::collections::HashMap;

use crate::utils::read_lines;

pub fn solution1() {
    let (mut id_list1, mut id_list2) = get_id_lists();

    id_list1.sort();
    id_list2.sort();

    let total_distance = id_list1
        .into_iter()
        .zip(id_list2)
        .map(|(left, right)| (left - right).abs())
        .sum::<i32>();

    println!("Total distance = {total_distance}");
}

pub fn solution2() {
    let (id_list1, id_list2) = get_id_lists();

    let id_count_map = id_list2
        .into_iter()
        .fold(HashMap::<_, i32>::new(), |mut map, id| {
            *map.entry(id).or_default() += 1i32;

            map
        });

    let similarity_score = id_list1
        .into_iter()
        .map(|id| id * id_count_map.get(&id).copied().unwrap_or_default())
        .sum::<i32>();

    println!("Similarity score = {similarity_score}");
}

fn get_id_lists() -> (Vec<i32>, Vec<i32>) {
    read_lines("src/day1/input.txt")
        .map(|line| {
            let mut ids = line.split_whitespace().map(|id| {
                id.parse::<i32>()
                    .expect("Ids from input must be valid integers")
            });

            (
                ids.next().expect("First Id on line must be present"),
                ids.next().expect("Second Id on line must be present"),
            )
        })
        .unzip()
}

I’m keeping my solutions up on GitHub.

Go

package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
	"strings"
)

func main() {
	input, _ := os.Open("input.txt")
	defer input.Close()

	left, right := []int{}, []int{}

	scanner := bufio.NewScanner(input)
	for scanner.Scan() {
		line := scanner.Text()
		splitline := strings.Split(line, "   ")
		l, _ := strconv.Atoi(splitline[0])
		r, _ := strconv.Atoi(splitline[1])
		left, right = append(left, l), append(right, r)
	}

	fmt.Printf("part 1 - total diff: %d\n", part1(left, right))
	fmt.Printf("part 2 - new total: %d\n", part2(left, right))
}

func part1(left, right []int) int {
	diff := 0
	sort.Ints(left)
	sort.Ints(right)

	for i, l := range left {
		if l > right[i] {
			diff += (l - right[i])
		} else {
			diff += (right[i] - l)
		}
	}
	return diff
}

func part2(left, right []int) int {
	newTotal := 0

	for _, l := range left {
		matches := 0
		for _, r := range right {
			if l == r {
				matches++
			}
		}
		newTotal += l * matches
	}
	return newTotal
}